U.S. Patent Publication No. 2011/0077876 discloses a tap for mounting on a container containing liquid, such as a wine box, a container containing medicine or a chemical, which tap comprises a sensor arranged on or in the tap for determining the outflow of liquid as a function of dispensing time and outflow characteristics. A display indicates the remaining amount of liquid in the container. The sensor may be a pressure sensor.
U.S. Patent Publication No. 2012/0097567 discloses an apparatus for managing the liquid volume in a container. The apparatus comprises a detector for detecting liquid volume changes in the container during a first preset period, a first determiner for determining whether the changes are lower than the first preset threshold value and a presenter for presenting the first prompt information in the case of the changes being lower than the preset threshold value. The device may include a pressure sensor and a tilt sensor.
It has long been recognized that it is important to maintain adequate levels of hydration particularly when carrying out physical exercise such as sport, hiking and so on. Even low levels of dehydration can have adverse physiological consequences. For instance, a 2% loss in bodyweight can reduce performance by 10-20%. A loss of fluid in excess of 3-5% of body weight reduces aerobic exercise performance noticeably and impairs reaction time, judgement, concentration and decision making. Dehydration can also place a strain on the cardiovascular system and can lead to heat stress and the inability of the body to adjust temperature by the normal sweat mechanisms.
Taking an excessive amount of fluid at any period, whether before the activity, during or after, often fails to ensure adequate hydration as the body is not able to store excess fluid or replenish lost fluid sufficiently quickly. It is best to take small amounts of fluids regularly over the course of the activity. For this purpose, athletes and others will often carry a source of fluid, traditionally in the form of a drinking bottle or cup but more recently by way of a hydration pack which can be kept in a backpack or similar bag. Hydration packs, or bladders as they are sometimes called, have proven very popular as they are comfortable to carry, are conformable in terms of shape, and have a low empty weight. A problem with such hydration packs, and any other liquid container which is flexible or not generally seen when used, is that it is difficult for the user to tell how much fluid they have consumed and how much fluid remains in the container. This results in difficulties in pacing fluid intake and as a result risks inadequate hydration during the period. It is not uncommon for such hydration packs to be used in environments where a ready supply of drinkable water is not available. In such circumstances, should the user run out of water this can cause dehydration and be potentially dangerous.
Flow meters are known for attachment to the outlet tube of a hydration pack but these can only provide a rough indication of fluid consumed, dependent upon the quality of fluid flowing through the outlet tube. A flow meter is not able to measuring remaining fluid in the pack.
A problem with hydration packs is that they are typically very flexible and may be held or carried in a variety of different ways by the user, making it difficult to obtain an accurate measurement of fluid in the pack.